Conventionally, it has been common that a printer is in one-to-one connection with a computer, while it is common recently that a printer is used as a so-called network printer shared by multiple computers via a network. When such a network printer is used, data to be printed (print data) flows through the shared network. Therefore, there is a possibility that the print data itself may be stolen, or, when the printer is away from a user, printed matter may be read or taken away by an unauthorized person during the time after the printed matter is outputted and before the user takes the printed matter. Accordingly, a technology for protection of security, a so-called secure printing technology, has been devised to protect data to be printed from an unauthorized person who has not given authorization to access the data.
To protect security of print data between a printer driver on a computer and a printer, encryption of data is performed. The printer driver performs encryption processing for all the print data, entire PDL data in the case of a PDL printer, to be sent to the printer before sending the data to the printer. The printer has to receive the encrypted PDL data, perform decryption processing, and then performs print processing based on the decrypted PDL data (for example, see Patent Document 1).
There has existed a technique for encrypting predetermined higher-order bits of image data or encrypting only predetermined print control commands included in print data to send the data to an image forming apparatus (Patent Document 2).
[Patent Document 1] Japanese Patent Laid-Open No. 2001-186358
[Patent Document 2] Japanese Patent Laid-Open No. 2000-276309